It is known in the surface cleaning art to utilize a rotating or oscillating brush to assist in removing dirt from a surface to be cleaned and transporting the dirt into a surface cleaning head of a vacuum cleaner, sweeper or the like. A rotary brush may be powered by an electric motor or an air turbine which may be drivingly connected to the brush by means of a fan belt or by directly mounting the brush on the shaft of the motor or air turbine so as to directly drive the brush from the electric motor or air turbine.
A rotary brush may occasionally become entangled with foreign objects, such as the fringes of an area rug, which cause the rotary brush to slow down or stop altogether. In such cases, the foreign object may be damaged by the strain applied to the object by the rotating brush when the brush becomes jammed. Alternately, or in addition, the motor drive means for the rotary brush may become damaged (the motor could overheat by drawing an excessive current due to the brush jam condition).
In some surface cleaning appliances, a rotary brush does not have a device to stop the brush rotating if the brush becomes jammed. However, mechanisms to terminate the rotation of a brush when a brush jam condition occurs are known. For example, it is known to use an electric circuit to monitor the current drawn up by an electric brush motor. When the brush becomes jammed, the current drawn by the brush motor increases. The circuit senses the rise in current drawn by the motor. The circuit may be programmed such that, upon a predetermined current rise, the brush motor is de-energized. Thus, the user is advised that the brush is jammed and may then clear the brush jam. One disadvantage to this approach is that additional electronics must be incorporated into a suction cleaner to monitor the current rise. This increases the cost of the surface cleaning appliance. In addition, due to the prevalence of dust and debris which enters the surface cleaning head, the electronics may become damaged or may malfunction. In addition, such a sensing circuit may not be used if the brush is driven by an air turbine.